Since it is an immutable rule that every individual host on an IP network must be assigned a unique IP address, which is used to communicate with other hosts on the same network or globally, it is now universally accepted that there … (As an aside, the IPng designers could not use version number 5 as a successor to IPv4, because it had been assigned to an experimental flow-oriented streaming protocol, Internet Stream Protocol ( ISP ) intended to support video and audio.

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Like it or Not, Here Comes IPv6 « Class in Session: CCNA